The virus was likely the same bug that has sickened hundreds on cruise ships and caused earlier outbreaks at Yellowstone and Grand Canyon national parks.

Of those who became sick, 53 were visitors and 81 were employees. Many of the workers were infected while cleaning up after sick visitors in a hotel room or living in close quarters at a dormitory, said Charles Higgins, director of the National Park Service’s Office of Public Health.

The outbreak was blamed on a norovirus. It sickens an estimated 23 million people every year, according to the Centers for Disease Control and Prevention. It is most commonly spread through eating contaminated food, touching contaminated surfaces and having direct contact with infected people.